I can't do the USD to Sterling currency conversion, but here is an idea.

Maybe they are charging you to regrind the old valves and seats and install new hardened valve seats in the heads for the 30-40# price you were quoted. As I suggested, I do not believe you need seats at all, and if so, ONLY exhaust. I would like to see close up shots of the seats AFTER the heads have been cleaned up professionally. In order to install new seats, the heads have to be cut first to accept the new seats, then recut to accept the valve profile. That is ALOT of labor and cost that can be avoided by an honest machinist.

As I stated, a SERDI cut (valve job) for the heads is roughly $175-$250 USD and the valves $5-10 USD each. For a total of $80-160 for cutting and cleaning old valves.

You do not need anything for the new valves (cut/grind) so the price you were quoted (40-50#) should be much lower. A SERDI valve job for the heads alone is all you will need with new valves.

You do not need, from looking at the pictures, new valve seats..which is a huge cost for both intake and exhaust. You only need the old valve seats in the heads recut. We only installed hardened intake and exhaust seats if the customer wanted larger valves OR the seat recession was clearly obvious. I have seen a handful of Pontaic heads that needed both intake AND exhaust hardened seats out of maybe 400 pairs. By a handful I mean maybe 5 to 10. I think your shop wants to get money from you that you do not need to spend.

Here is a breakdown in what my shop charges in US dollars.

Disassemble heads, bake, shotblast, magnaflux $100
SERDI valve job $225
Comp Cams springs, retainers and locks $175-225
New guides $10 each, Machine for giudes another $5
Valves $125-200 (depending on quality)
Set up spring height and assemble $125-175

Includes valve stem seals.

You should be able, from looking at those pictures, be able to have those heads perfect for around $750-900 USD.

Those heads, to address the rust and condition...After a bake and shotblast, will look like new.

The 9777755 is a 68 Firebird left manifold...Be just fine with a 326.